Photon Counting System Research Articles

Scanning microradiographic studies of rates of in vitro demineralization in human and bovine dental enamel

The aim was to measure frequently and with precision the local integrated mineral loss through small areas of the natural surface of human and bovine enamel during in vitro demineralization using an X-ray photon-counting system (scanning microradiography). The method used was an adaptation of photographic longitudinal microradiography in which the attenuation of X-rays through the enamel is measured in the direction of acid attack, i.e., normal to the enamel surface. The mass of mineral (assumed to be hydroxyapatite) per unit exposed area was measured over 15 μm dia. circles at a series of positions as a function of time in blocks of human and bovine enamel immersed in 0.1 mol/l acetic acid buffered to pH 4.0 with NaOH. There was an initial period (approx. 45 h for human, approx. 75 h for bovine enamel) during which the mineral loss with time was sigmoidal, followed by a nearly linear loss for the remainder of the experiment, in some cases up to 500 h. The initial sigmoidal period may be due to properties of surface enamel or be associated with the development of a surface layer overlying subsurface demineralization. The essentially constant rate of mineral loss after the surface layer has formed confirms earlier observations and is consistent with a rate-limiting process occurring at the dissolving enamel surfaces of the advancing front, and not by transport of ions within the lesion. Small perturbations from a linear loss were seen, which were approximately periodic for human enamel. The slope of the linear period was rather constant within one human or bovine block, but variable between blocks without a clear distinction between human and bovine enamel.

Bioluminescence under static magnetic fields

In the present study, the effect of magnetic fields on the emission of light by a living system was studied. The fireflies Hotaria parvula and Luciola cruciata were used as the bioluminescence systems. The firefly light organ was fixed at the edge of an optical fiber. The emitted light was introduced into a single-channel photon-counting system using an optical fiber. We measured both the spectrum of a constant light emission and, the time course of bioluminescence pulses. Two horizontal-type superconducting magnets, which produced 8 and 14 T magnetic fields at their center, were used as the magnetic-field generators. We also carried out an in vitro study of bioluminescence. The enzymatic activity of luciferase was measured under a 14 T magnetic field. We measured emission spectra of bioluminescence over the interval 500–600 nm at 25 °C in a stable emission state. It was observed that the peak wavelength around 550 nm shifted to 560 nm under a 14 T magnetic field. However, the effects of magnetic fields were not significant. Also, we measured the time course of emissions at 550 nm in a transient emission state. The rate in the light intensity under a 14 T magnetic field increased compared to the control. There is a possibility that the change in the emission intensities under a magnetic field is related to a change in the biochemical systems of the firefly, such as the enzymatic process of luciferase and the excited singlet state with subsequent light emission.

Combination of synchrotron radiation and laser for two-photon spectroscopy of BaF2

Abstract We have carried out nonlinear spectroscopy by making use of tunable VUV light from synchrotron radiation (SR) together with intense light from a laser. The valence excitons of BaF 2 with a large band gap of ∼11 eV were chosen as our target. A single crystal of BaF 2 was irradiated at 15 K by the two light pulses from the SR (6–9 eV) and an Nd : YAG laser (2.33 eV). Self-trapped exciton luminescence induced by two-photon excitation was detected with a time-gated photon-counting system developed for the present study. This zero-method technique is expected to be sensitive compared to early experiments by an Italian group monitoring transmittance changes. The obtained two-photon spectrum shows a distinct band below the band gap energy. This band includes two contributions, a two-step cascade process and a two-photon absorption process. The energy of the 2 P exciton is estimated to be 10.6 eV at 15 K.

A new toroidal electrostatic analyzer and application to surface analysis

A new toroidal electrostatic analyzer (ESA) configuration for medium energy ion scattering has been designed and fabricated for structural analysis of surfaces. The present analyzer has a wide interelectrode distance of 16 mm and an energy range of 10% of the pass energy at a constant applied voltage. The analyzer is mounted horizontally on a turntable and accepts ions scattered within a well defined angular range. To get a good energy resolution, we employed a photon-counting image acquisition system (PIAS: Hamamatsu Photonics) with spatial resolution of 40–50 μm, combined with a three-stage microchannel plate. The electric fields of the toroidal ESA including the fringing fields were calculated by a finite element method. Ion trajectories through the analyzer were calculated using a Monte Carlo method. In this way, the optimum conditions of the geometry and size of the entrance and exit slits were determined. Our toroidal analyzer resolved three surface peaks from the Si isotopes (Si28, Si29, and Si30) clearly in the aligned spectra from H-terminated Si(001) and Si(111) and the energy resolution (ΔE/E) was estimated to be about 1×10−3. We describe the notable features of the new setup of the toroidal analyzer and show direct detection of H on Si(001) and Si(111) as a typical application.

Subpixel sensitivity map for a charge-coupled device sensor

The sensitivity across a solid state detector array varies as a result of differences in transmission, diffusion and scattering properties over the sensor. This variation will occur over a range of scale lengths and its knowledge is of importance for improved device design and in a variety of applications, for example, event centroiding in photon counting systems. A measurement of the sensitivity variation on a subpixel scale for a two-phase front-illuminated CCD is reported. The measurement is made using a scanning reflection microscope. A variation in sensitivity between the phases within a pixel is clearly observed, as well as varia- tions on a much smaller spatial scale. © 1998 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(98)03103-1) Subject terms: charge-coupled device; pixel sensitivity; response function; crosstalk.

Chemiluminescence of cereal products III. Two-dimensional photocount imaging of chemiluminescence.

Two-dimensional (2-D) spatial distributions of ultra-weak chemiluminescence (photon imaging) from auto-oxidizing and water-hydrated cereal food products were measured by means of a high-sensitivity 2-D photon counting system--an intensified charge coupled device (CCD) camera. The 2-D images obtained reveal the dynamics and emission patterns of very slow auto-oxidation reactions and much faster processes of water penetration into cereal products. The enhancement of chemiluminescence by the addition of water appears to involve complex processes with an inhomogenous spatial and energy distribution within cereal products. The effect of antioxidants, free radical promoters and scavengers suggests that oxidative radical reactions contribute significantly to the observed chemiluminescence. The possible involvement of hydrophilic interactions, H2O-biopolymers and recombination of trapped radicals is also discussed.

Chemiluminescence of cereal products. III. Two‐dimensional photocount imaging of chemiluminescence

Two-dimensional (2-D) spatial distributions of ultra-weak chemiluminescence (photon imaging) from auto-oxidizing and water-hydrated cereal food products were measured by means of a high-sensitivity 2-D photon counting system—an intensified charge coupled device (CCD) camera. The 2-D images obtained reveal the dynamics and emission patterns of very slow auto-oxidation reactions and much faster processes of water penetration into cereal products. The enhancement of chemiluminescence by the addition of water appears to involve complex processes with an inhomogenous spatial and energy distribution within cereal products. The effect of antioxidants, free radical promoters and scavengers suggests that oxidative radical reactions contribute significantly to the observed chemiluminescence. The possible involvement of hydrophilic interactions, H2O-biopolymers and recombination of trapped radicals is also discussed. © 1998 John Wiley & Sons, Ltd.

List-mode likelihood.

As photon-counting imaging systems become more complex, there is a trend toward measuring more attributes of each individual event. In various imaging systems the attributes can include several position variables, time variables, and energies. If more than about four attributes are measured for each event, it is not practical to record the data in an image matrix. Instead it is more efficient to use a simple list where every attribute is stored for every event. It is the purpose of this paper to discuss the concept of likelihood for such list-mode data. We present expressions for list-mode likelihood with an arbitrary number of attributes per photon and for both preset counts and preset time. Maximization of this likelihood can lead to a practical reconstruction algorithm with list-mode data, but that aspect is covered in a separate paper [IEEE Trans. Med. Imaging (to be published)]. An expression for lesion detectability for list-mode data is also derived and compared with the corresponding expression for conventional binned data.

Chest wall thickness measurements of the LLNL and JAERI torso phantoms for germanium detector counting. Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute.

The Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute torso phantoms were developed to calibrate lung counting systems that are used to estimate plutonium and other radionuclides deposited in the lung. Originally, low energy photon counting systems consisted of phoswich detectors. The average chest wall thicknesses and individual measurement points of the Lawrence Livermore National Laboratory phantom and its overlay plates in the regions covered by these detectors were provided by the manufacturer. Germanium detectors are of a different size and are placed in different locations on the phantom so that the manufacturer's data are no longer applicable for the locations of the germanium detectors on the phantom. The Human Monitoring Laboratory has re-evaluated the chest wall thickness of both the Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute phantoms and their overlay plates for its germanium lung counting system. The measurements were made in the upper right, lower right, upper left, and lower left positions on the phantom's torso plate above the lungs. The effective chest wall thicknesses (17 keV) for the Lawrence Livermore National Laboratory torso plate are 1.46 cm, 1.43 cm, 1.66 cm, 1.48 cm, respectively. The manufacturer's quoted average effective chest wall thickness for a pair of phoswich detectors is 1.63 cm. The measured effective chest wall thicknesses (17 keV) for the JAERI's torso plate are 1.76 cm, 2.15 cm, 1.79 cm, 2.15 cm, respectively. The manufacturer's quoted average chest wall thickness for an unspecified region of the chest is 1.50 cm. This paper presents effective chest wall thickness data for the phantoms with and without their overlay plates at 17 keV, 60 keV, 200 keV and 1,500 keV. The uncertainties involved in determining the effective chest wall thickness have shown that there is no significant difference between the effective chest wall thickness and the physical chest wall thickness.

Fast fluorescence decay of naphthalene induced by Ar ion irradiation

A single photon counting system was constructed for a time resolved fluorescence measurement with pulsed heavy ions from the AVF cyclotron in Takasaki Ion Accelerators for Advanced Radiation Application (TIARA). Fluorescence spectra and decay of naphthalene in poly(vinyl butylal) (PVB) film were observed from the irradiation with Ar ions. Though fluorescence spectra were assigned to the first singlet excited state of naphthalene, the decay with Ar ion irradiation were faster than that excited by UV light. This faster decay results from quenching by the transient species produced. The relative initial concentration of the excited state of naphthalene to that of the radicals increases with increasing energy deposited along the incident ion's trajectory.

Preferential degradation of plastid DNA with preservation of mitochondrial DNA in the sperm cells ofPelargonium zonale during pollen development

In the present study, we studied changes in organellar DNA in the sperm cells of maturing pollen ofPelargonium zonale, a plant typical to exhibit biparental inheritance, by fluorescence microscopy after staining with 4′,6-diamidino-2-phenylindole (DAPI) and by immunogold electron microscopy using anti-DNA antibody. Fluorescence intensities of DAPI-stained plastid nuclei in generative and sperm cells at various developmental stages were quantified with a video-intensified microscope photon counting system (VIMPCS). Results indicated that the amount of DNA per plastid in generative cells increased gradually during pollen development and reached a maximum value (about 70 T per plastid; 1 T represents the amount of DNA in a particle of T4 phage) in young sperm cells at 5 days before flowering. However, the DNA content of plastids was subsequently reduced to about 20% of the maximum value on the day of flowering. Moreover, the DNA content of the plastid further decreased to 4% of the maximum value when pollen grains were cultured for 6 h in germination medium. In contrast, the amount of DNA per mitochondrion did not decrease significantly around the flowering day. Similar results were also obtained by immunogold electron microscopy using anti-DNA antibody. The density of gold particles on plastids decreased during pollen maturation whereas labelling density on mitochondria remained relatively constant. The number of plastids and mitochondria per generative cell or per pair of sperm cells did not change significantly, indicating that the segregation of DNA by plastid division was not responsible for the decrease in the amount of DNA per plastid. These results indicate that the plastid DNA is preferentially degraded, but the mitochondrial DNA is preserved, in the sperm cells ofP. zonale. While the plastid DNA of the sperm cells decreased before fertilization, it was also suggested that the low DNA contents that remain in the plastids of the sperm cells are enough to account for the biparental inheritance of plastids inP. zonale.

Fluorescence lifetime imaging of experimental tumors in hematoporphyrin derivative-sensitized mice.

Tumor detection has been carried out in mice sensitized with hematoporphyrin derivative (HpD) by measuring the spatial distribution of the fluorescence lifetime of the exogenous compound. This result has been achieved using a time-gated video camera and a suitable mathematical processing that led to the so-called "lifetime images." Extensive experimental tests have been performed on mice bearing the MS-2 fibrosarcoma or the L1210 leukemia. Lifetime images of mice show that the fluorescence decay of HpD is appreciably slower in the tumor than in healthy tissues nearby, allowing a reliable detection of the neoplasia. The lengthening of the lifetime in tumors depends little on the drug dose, which in our experiments could be lowered down to 0.1 mg/kg body weight, still allowing a definite tumor detection. In order to ascertain the results achieved with the imaging apparatus, high-resolution spectroscopy, based on a time-correlated single photon counting system, has also been performed to measure the fluorescence lifetime of the drug inside the tumor and outside. The outcomes obtained with two techniques are in good agreement.

A large area, 2-D, high-pressure MWPC for wide angle X-ray diffraction

Multi Wire Proportional Counters (MWPCs) possess all the required features for recording X-ray diffraction patterns: large area, high detective quantum efficiency (DQE), low dead time and simultaneous spatial and spectral information. However, their suitability as wide-angle diffraction is compromised by an effect known as parallax broadening. This phenomenon is due to the low density of the gas in the detector, where photons incident at large angles following the same ray may interact at different points along it and therefore appear as different coordinates in the image. One way to reduce this effect is by increasing the density of the absorbing medium in order to ensure the photons interact in a thinner gas layer, this can be achieved if the pressure of the gas in the detector is increased. We present here a high-pressure (5 bar) detector which has the potential to bring the desirable features of a photon counting system to wide-angle diffraction experiments. The preliminary results are also presented.

Tip localized Ca2+ pulses are coincident with peak pulsatile growth rates in pollen tubes of Lilium longiflorum.

It is known that locally elevated Ca2+ at the growing tips of pollen tubes is necessary for pollen tube elongation. Here we show that this localized Ca2+ is also temporally regulated and is closely associated with pulsatile tip growth. Lilium longiflorum pollen tubes were injected with the photoprotein, aequorin, and the Ca2(+)-dependent light output was detected with a low noise photon-counting system. Ca2+ pulses with a mean period of 40 seconds were invariably associated with growth. The pulses were sporadic and of low amplitude for about the first 1.5 hours after germination. With subsequent growth, pulses increased in amplitude and the period between pulses became more regular. We have localized these Ca2+ pulses to the elongating end of the growing tube. The Ca2+ pulses are asymmetrical, rising more slowly than they fall. We estimate that the Ca2+ concentration at the peak of the pulses reaches nearly 10 microM. The addition of 100 microM La3+, a Ca2+ channel blocker, extinguished the pulses. An analysis of growth of elongating tubes establishes that extension is pulsatile, with a 42 second period between pulses. Calcium imaging, using the fluorescent indicator, Calcium Green dextran, shows that calcium pulses are coincident with peak growth rates.

Measurement of chemiluminescence from neutrophils in a 96-well microplate using Lumi Box U-800 II.

We have developed a microplate photon counting system based on a cooled charge-coupled device (Lumi Box U-800 II) jointly with Maikurotekku Nition Company (Chiba, Japan). The system makes it possible to quantify chemiluminescence (CL) in a 96-well microplate automatically and simultaneously in a single experiment. We studied the measurement conditions for a luminol-dependent CL assay from neutrophils stimulated with opsonized zymosan (OZ) using this system. Parameters examined included the effect of OZ dose per well, mixing speed, mixing time and detection time on CL responses. The results indicated that this system allows the measurement of CL from phagocytes on a large number of samples using small amounts of sample and regents.

Imaging chemiluminescence instrument for the study of heterogeneous oxidation effects in polymers

An imaging Chemiluminescence equipment used for studies of diffusion controlled oxidation effects in polymers is presented. The design involves an imaging photon counting system mounted on a cylindrical oven with a controlled atmosphere. The overshoot on heating is less than 2 °C and the temperature during isothermal conditions is maintained at ±0.4 °C, thus, a stable thermal environment is attained. To point out possible applications, the monitoring of oxidation profiles from aged nylon specimens and oxygen-barrier properties of an inorganic coating by chemical plasma deposition on a hydroxyl terminated polybutadiene substrate are presented. The results demonstrate the feasibility of studying diffusion controlled oxidation and also the possibility of the technique to estimate the function and durability of surface treatments on elastomers.

Measurement of changes in sarcoplasmic reticulum [Ca 2+] in rat tail artery with targeted apoaequorin delivered by an adenoviral vector

The physiologic relevance of Ca 2+ release from the sarcoplasmic reticulum in arterial smooth muscle contraction is controversial. Therefore, we sought to measure changes in sarcoplasmic reticulum free [Ca 2+] (i.e. [Ca 2+] sr) in the intact rat tail artery. We exploited a novel technique to measure [Ca 2+] sr with genetically targeted apoaequorin acting as a pseudo-luciferase rather than as classic aequorin. Intact rat tail arteries were infected with a replication deficient adenoviral vector (RAdER) containing the apoaequorin gene targeted to the sarcoplasmic reticulum. Addition of apoaequorin's substrate, coelenterazine, to the perfusate increased light production in a [Ca 2+] dependent manner, consistent with apoaequorin action on coelenterazine. Within the limits of the photon counting system, imaging of infected rat tail artery segments revealed light production from the whole thickness of the vascular wall. Phenylephrine stimulation decreased apoaequorin generated light and induced a contraction. Washout of phenylephrine relaxed the tissues and increased light indicating refilling of the sarcoplasmic reticulum with Ca 2+. Incubation in 10 μM cyclopiazonic acid, a SERCA inhibitor, did not alter apoaequorin generated light or induce a contraction. In the presence of cyclopiazonic acid, phenylephrine contractions were enhanced and apoaequorin generated light decreased further than that observed in the absence of cyclopiazonic acid. Cyclopiazonic acid also prevented the increase in apoaequorin generated light upon washout of phenylephrine, consistent with its inhibition of sarcoplasmic reticulum refilling. These results suggest that light production from targeted apoaequorin, delivered by a replication deficient adenovirus, is a valid measure of changes in [Ca 2+] sr in the intact arterial wall. There appeared to be a correlation between Ca 2+ release and contraction in these lightly loaded arteries.

Fluorescence correlation spectroscopy with traveling interference fringe excitation

A new improved fluorescence correlation spectroscopy method for determining motional states of particles, fluorescence correlation spectroscopy with traveling interference fringe excitation (FCSTFE), is described. With this method the modulated fluorescence signal from particles excited by an interference fringe moving at constant velocity is detected, and cosine and sine Fourier coefficients at the frequency of the traveling fringe [Fcos(t), Fsin(t)] are recorded. Autocorrelation functions of Fcos(t), Fsin(t), and the square of amplitude [A2(t)=Fcos(t)2+Fsin(t)2] were found to express the motion of the fluorescent particles. The apparatus utilizing a photon counting system was constructed, and the performance of the system was demonstrated by the determination of diffusion coefficients of dispersed fluorescent polystyrene spheres. Features of FCSTFE in particle dynamics evaluation are discussed.

Scanning near-field optical/atomic force microscopy for fluorescence imaging and spectroscopy of biomaterials in air and liquid: Observation of recombinantEscherichia coli with gene coding to green fluorescent protein

We have developed a system of scanning near-field optical/atomic force microscopy (SNOM/AFM) for fluorescence imaging and spectroscopy of biomaterials in air and liquid. SNOM/AFM uses a bent optical fiber simultaneously as a dynamic force AFM cantilever and a SNOM probe. Optical resolution of SNOM images shows about 50 nm in an illumination mode for a standard sample of a patterned chromium layer of 20 nm thickness on a quartz glass plate. The SNOM/AFM system contains a photon counting system and polychrometer/ICCD (intensified charge coupled device) system for observation of the fluorescence image and spectrograph of micro areas, respectively. The gene coding to green fluorescence protein (GFP) was cloned in recombinantEscherichia coli (E. coli). Topography, fluorescence image and spectrograph of recombinantE. coli by SNOM/AFM showed a difference in fluorescence in individualE. coli. Fluorescence activity of GFP can thus be used as a convenient indicator of transformation. SNOM/AFM is also applicable to observe immobilizedE. coli on a glass plate in water with a liquid chamber and may allow the viewing of observation of floating organisms.

Observation of photon emissions from hot electrons and latch-up at the cleaved surface of CMOS structures

Hot-electron-induced and latchup-induced photon emissions can be directly observed from the cleaved surface of CMOS test structures using a two-dimensional photon counting system. Observations of an NMOSFET under near-drain-breakdown conditions revealed the location and intensity profile of both hot-electron-induced photon emissions and also carrier recombination radiation arising from bipolar action caused by impact ionization. In addition, the photon intensity profile of latch-up-induced emissions clearly showed two peaks. The observation of a cleaved surface makes it possible to determine the exact location of photon emissions because the aluminum electrode does not mask them.